CAPTURE GAMMARAY SPECTROSCOPY AND RELATED TOPICS: 12th International Symposium

K‐Isomers and Aspects of Nuclear Structure
View Description Hide DescriptionGamma‐ray spectroscopy measurements with Gammasphere and multi‐nucleon transfer reactions with heavy beams provide a means of accessing deformed nuclei at stability, or on the neutron‐rich side of the stability line. New results on the discovery of high‐K isomers in the Er‐Tm‐Yb‐Lu region are discussed with a focus on the energy systematics and the factors which may govern K‐purity and therefore K‐hindrances. These include random‐mixing in regions of high level density, specific Coriolis mixing in configurations involving the i_{13/2} neutron configuration, and chance degeneracies between an individual high‐K state and a specific collective state which provide an opportunity to extract effective mixing matrix elements between states of very different‐K.

In‐Beam γ‐Spectroscopy of Low‐Spin Mixed‐Symmetry States of ^{138}Ce with Gammasphere in Singles‐Mode
View Description Hide DescriptionGamma‐rays from the nuclide ^{138}Ce have been measured with the Gammasphere‐array following Coulomb excitation. Beams of ^{138}Ce ions were focussed on a carbon target at beam energies of 480 and 400 MeV. Gamma‐ray yields and relative Coulomb excitation cross sections were measured in singles‐mode. M1, E2, and E3 transition matrix elements from low‐spin states were measured relative to the known . The M1 strength distribution from the lowest six 2^{+} states up to 2.7 MeV enables us to identify the state of ^{138}Ce as the dominant fragment of the one‐phonon mixed‐symmetry state with F‐spin quantum number F _{max} − 1. From its mixing with the nearby state an F‐spin mixing matrix element of 44 keV can be estimated.

Nuclear isomers: stepping stones to the unknown
View Description Hide DescriptionThe utility of isomers for exploring the nuclear landscape is discussed, including their role in superheavy‐element research, and the possibility of observing neutron radioactivity. Emphasis is given to K isomers in deformed nuclei. Transition rates are examined in the N_{p}N_{n} scheme for 2‐ and 3‐quasiparticle K‐isomer decays, and in connection with level densities for higher quasiparticle numbers.

Violations of K‐Conservation in ^{178}Hf
View Description Hide DescriptionCoulomb excitation of K ^{π}=6^{+}(t_{1/2}=77 ns), 8^{−}(t_{1/2}=4.0 s) and 16^{+}(t_{1/2}=31 y) ^{178}Hf isomers has led to the measurement of a set of Eλ matrix elements, coupling the isomer bands to the γ‐ and ground state bands. The resulting matrix elements, derived using a coupled‐channel semiclassical Coulomb excitation search code, have been used to probe the K‐components in the wave functions and revealed the onset and saturation of K‐mixing in low‐K bands, whereas K‐mixing is negligible in the high‐K bands. The implications can be applied to other quadrupole‐deformed nuclei. An upper limit on the Coulomb depopulation yield of the 16^{+} isomer was calculated based on the present set of matrix elements.

Theoretical Description of K‐Isomers
View Description Hide DescriptionA proper treatment of K‐mixing is the key to understanding K‐isomers. Here, we present a method based on the projected shell model. This method differs from the usual description of multi‐quasiparticle states by introducing a transformation to the laboratory frame and a subsequent configuration mixing in that frame. It allows a quantitative study on the degree of K‐violation through direct calculations of electromagnetic transitions.

Isomer and In‐Beam Spectroscopy of Medium‐Spin States in ^{91,92}Zr
View Description Hide DescriptionNear‐yrast states have been identified in the stable ^{91,92}Zr isotopes using the fusion evaporation reaction ^{82}Se(^{13}C,xn)^{95−x}Zr at an incident beam energy of 50 MeV. Gamma‐ray spectroscopy of states above the reported τ = 6 μs, isomer in ^{91}Zr are reported for the first time with consequences for stimulating new shell model calculations which incorporate either the breaking of the N=50 shell closure and/or the inclusion of the negative parity h_{11/2} neutron intruder orbital.

Dave Warner: Friend, Mentor, Colleague
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Emerging Collectivity in Nuclei, Shape Coexistence, and Proton‐Neutron Interactions
View Description Hide DescriptionThe growth of collectivity and phase transitional behavior in nuclei is one of the central questions facing nuclear structure studies today and in the future, especially with the advent of new generation facilities for the study of exotic nuclei. The role of the valence p‐n interaction is key. Several new developments relating to these issues will be discussed. A new interpretation of the light Pt isotopes without the need for intruder states is related to the choice of single and multiple Hilbert spaces in the description of spherical‐deformed transition regions. A new set of empirical proton‐neutron interactions, extracted from double differences of atomic masses, shows striking bifurcations near closed shells, a generic relation to shell £lling, and an empirical correlation to the different growth rates of collectivity in particle‐particle and particle‐hole regions. Finally, an extensive series of (p,t) experiments to locate 0^{+} states in a broad range of transitional and deformed nuclei has disclosed a number of new features of these modes ranging from evidence from non‐collective degrees of freedom to the statistics of nearest neighbor spaces and a new signature for critical point nuclei.

Symmetry and Wigner Energy in Nuclear Matter
View Description Hide DescriptionThe nature of the symmetry and Wigner energy in the nuclear mass formula is studied. It is shown that their effects are intertwined and that one term cannot be reliably determined without knowledge of the other. This leads to considerable uncertainty in the value for the symmetry energy that should be adopted in nuclear matter.

Varying shell structure in sd‐pf nuclei
View Description Hide DescriptionRecent experiments on exotic nuclei with N=18 and 19 are discussed in connection to the variation of the shell gap at N=20. It is suggested that the gap is really small in such exotic nuclei. We show how the gap can be calculated from the shell‐model interaction SDPF‐M. Its characteristic feature can be explained as a effect of the tensor force. Thus, one of the subjects Dave Warner has been studying opens a new field of nuclear structure physics.

Recent advances in studies of mirror‐symmetry in the A=40–56 shell
View Description Hide DescriptionThe study of mirror symmetry has been extended to the T_{ z }=±1/2 nuclei ^{45}V and ^{45}Ti using a ^{24} Mg + ^{24} Mg fusion‐evaporation reaction at the Vivitron accelerator at IReS Strasbourg. In order to extend the study to more‐exotic nuclei, a new experimental technique using fragmentation of a secondary beam has been tried at GSI. The aim was to study excited states in ^{53} Ni using fragmentation of a ^{55} Ni beam produced in the initial fragmentation of 600 MeV/A ^{58} Ni by a ^{9}Be target. Details and results of both experiments will be presented.

Measurement of Parity‐Violating Gamma‐ray Asymmetry in Compound Nuclei with Cold Neutrons
View Description Hide DescriptionThe NPDGamma collaboration has constructed and commissioned an apparatus on flight path 12 at LANSCE to measure with a high precision, 5×10^{−9}, the small parity‐violating gamma‐ray asymmetry, A _{γ}, in polarized neutron capture on protons. This asymmetry can be determined unambiguously the weak pion‐nucleon coupling constant. To study the hadronic weak interaction at low energy, the collaboration has used the NPDGamma apparatus to measure parity‐violating gamma‐ray asymmetries in compound nuclei with cold neutrons. Using the statistical model of compound nuclei and spectroscopic information of the target nuclei, we can set upper limit on the spreading width of the hadronic weak interaction for intermediate‐mass nuclei. We describe the experiment and the preliminary results of measured gamma‐ray asymmetries of Al, Sc, Ti, Mn, and Co.

Scattering Of KeV Neutrons And The Problem Of Quantum Entanglement
View Description Hide DescriptionA scattering study of ∼ 30 keV neutrons from H_{2}O, D_{2}O and H_{2}O/D_{2}O mixtures was carried out to search for a ∼ 40% anomalous drop in the n‐p scattering cross section. Such an anomaly was reported using 10–200eV neutrons scattered from many H‐containing compounds. The anomaly was attributed to n‐scattering from quantum entangled proton pairs in the sample. In the present measurement no anomaly was observed.

Random Matrix Thermodynamics
View Description Hide DescriptionWe have performed a study of the statistical mechanics of correlated spectra first introduced by Dyson and Mehta some 40 years ago. We have derived a modified thermodynamical statistics (a number and its variance) for linear spectra. This approach was used to analyze the statistical properties of the eigenvalues of random matrices of Gaussian ensembles and of the experimental eigenfrequencies of acoustic resonances of an aluminum plate cut in the shape of a chaotic billiard. The results obtained suggest that this statistics provides a robust tool for the investigation of spectral properties.

Symmetry of Isoscalar Matrix Elements and Systematics in the sd and beginning of fp shells
View Description Hide DescriptionA careful determination of the lifetime and measurement of the branching ratio for decay of the first state in ^{42}Sc has allowed an accurate experimental test of charge independence in the A = 42 isobaric triplet. A lifetime of 69(17) fs was measured at the University of Kentucky, while relative intensities for the 975 keV and 1586 keV transitions depopulating the first state have been determined at the University of Cologne as 100(1) and 8(1), respectively. Both measurements give an isoscalar matrix element, M _{0}, of 6.4(9) (W.u.)^{1/2}. This result confirms charge independence for the A=42 isobaric triplet. Shell model calculations have been carried out for understanding the global trend of M _{0} values for A = 4n + 2 isobaric triplets ranging from A = 18 to A = 42. The transition energies, reduced transition probabilities and M _{0} values are reproduced to a high degree of accuracy. The trend of M _{0} strength along the sd shell is interpreted in terms of the shell structure. Certain discrepancies arise at the extremes of the sd shell, for the A = 18 and A = 38 isobaric triplets, which might be explained in terms of the low valence space at the extremes of the sd shell.

Symmetry and structure tests in ^{18}O and ^{18}Ne
View Description Hide DescriptionIsospin (T) symmetry assumes charge symmetry and charge independence are explicit in nuclear structure. Whereas charge independence implies the nn, np and pp interactions are the same, charge symmetry states that the nn and pp interactions are equal. The latt_er approximate symmetry is experimentally verified by the comparison of the excited levels lying at about the same energy in light mirror nuclei. Both of these symmetries are broken by the electromagnetic interaction. The neutron facility at the University of Kentucky provides a unique opportunity to examine charge independence, and in particular, charge symmetry from the reduced electromagnetic transition probabilities and neutron scattering cross sections. Here, we use the isospin formalism by Bernstein, Brown and Madsen, which relates the proton and neutron matrix elements, M _{p} and M _{n} respectively, for equivalent excited states in T=1 mirror nuclei (T_{z} = +/−1). The nucleus ^{18}O has been studied using the (n,n′) reaction in order to measure the neutron cross sections of the , T=1 state. Using the previously determined proton matrix elements for the T_{z} = −1 mirror nucleus (^{18}Ne), along with the determination of the neutron matrix element in ^{18}O from neutron scattering, allows an experimental test of charge symmetry in the A=18 mirror system.

Gamma‐Ray Transitions In the Decay of the Superallowed Beta Emitter ^{62}Ga
View Description Hide DescriptionA measurement of the ground state β‐decay branching ratio of ^{62}Ga has been made as part of a program of high‐precision superallowed Fermi β decay studies at the ISAC radioactive beam facility. The experiment was conducted by detecting γ rays and β particles from the decay of ^{62}Ga using the 8π γ‐ray spectrometer and the SCEPTAR plastic scintillator array.

Nuclear Structure and Decay Data: Current Status and Future Perspectives
View Description Hide DescriptionThe nuclear structure databases provide physicists around the world with a useful collection of reliable and well documented datasets. The Evaluated Nuclear Structure Data File (ENSDF) database, produced by the International Nuclear Structure and Decay Data Network (NSDD) under the auspices of the International Atomic Energy Agency (IAEA), contains evaluated experimental information for all known nuclei. The bibliographical database Nuclear Science References (NSR) provides references to published data in the field of Nuclear Physics. The Experimental Unevaluated Nuclear Data List (XUNDL) provides a method for rapid access to formatted (compiled) data from recently published articles. Detailed information regarding these databases, as well as other products and services, can be found at the National Nuclear Data Center (NNDC) and IAEA web portals.

An Updated Library of Reaction Rates for the Astrophysical rp‐Process
View Description Hide DescriptionWe are developing an updated library with reaction rates important for the study of the astrophysical rp‐ process. It includes both experimental and theoretical rates parametrized in terms of the standard REACLIB format. The experimental data contain various compilations updated with the most recent data. The theoretical data are taken from shell‐model calculations whenever available otherwise statistical Hauser‐Feshbach calculations were used. All theoretical rates were recalculated using the latest reaction Q‐values. All new rates include stellar enhancement factors. The data will be accessed through a convenient web interface. It is anticipated that this JINA project evolves into an evaluated public data archive for reaclib library data.